57
with arylboronic acids by using Pd(OAc) 2 as the catalyst and Ag 2 CO 3 as the oxidant (Scheme 3.22) [70]. The key to access a broad substrate scope with respect to
both polyfluorobenzenes and arylboronic acids is the choice of bases depending
on acidities of the polyfluorobenzenes.
Apart from noble metal catalysis, the first-row transition-metal catalysts (e.g.,
Mn, Ni, Cu, Fe) can also be applied in oxidative cross-coupling reactions. As early
as 2003, Demir and co-workers developed an oxidative cross-coupling between
simple arenes and arylboronic acid mediated by Mn(OAc) 3 (Scheme 3.23) [71]. The
H
Pd(OAc) 2 (5 mol%)
o-chloranil (1 equiv)
DCE, 80
o C
O
B
3
FeCl 3 (5 equiv)
CH 2 Cl 2 / MeNO 2
0
o C to rt
60%
Scheme 3.20 Synthesis of extended PAHs
+
(HO) 2 B Ar
Pd(OAc) 2 (10 mol%)
bpy (10 mol%)
TEMPO (4 equiv)
C 6 H 5 CF 3 , 80
o C, 12 h
S
R 2
R 1
H
H
S
R 2
R 1
Ar
S
Et
51%
F
S
Et
89%
Me
S
Me
65%
S
nC 6 H 13
82%
S
Cl
53%
S
Me
79%
Me
S
Ph
87%
MeO
S
92%
+
S
R 2
R 1
Ar
trace
1 equiv
4 equiv
Scheme 3.21 Pd-catalyzed oxidative C4-arylation of thiophenes with arylboronic acids
3 Oxidative Coupling Reactions Between Hydrocarbons and Organometallic Reagents…